The disclosed invention is generally directed to infrared image sensing arrays, and is more particularly directed to an infrared image sensing array architecture having first and second subarrays respectively responsive to different brightness ranges.
Infrared image sensing arrays typically include an array of solid-state detector elements, commonly called pixels, arranged in rows and columns. Readout circuitry senses the amount of radiation received by the respective elements and provides output signals indicative of the received radiation. The outputs of the readout circuitry, which typically includes sensing circuits associated with the detector elements and output buffers, are provided to further circuitry for analog-to-digital conversion and processing.
Infrared image sensing arrays are commonly fabricated as hybridized detector/readout assemblies which include a generally planar integrated circuit detector assembly comprising the detector elements, and a generally planar integrated circuit readout circuit assembly comprising the sensing circuits and the readout buffers. The assemblies are mechanically secured to each other in layered fashion with appropriate electrical interconnection of the circuits on the respective assemblies. For example, the readout circuitry would include respective sensing circuits for each of the detector elements, and respective output buffers associated with the sensing circuits for each column, whereby the sensing circuit outputs for a given column would be multiplexed to the associated output buffer.
Ideally, infrared image sensing arrays would provide fast operation, dissipate little power and have a wide dynamic range. However, known implementations of infrared imaging arrays generally involve tradeoffs due to factors which cannot be avoided, including for example parasitic capacitances in the detector array itself as well as in the connecting wires that couple the readout outputs to the analog-to-digital conversion circuitry. Faster speed and/or greater dynamic range requires more power, which in turn requires more cooling capacity. Greater dynamic range further requires more complex processing components. The implications of greater power and cooling requirements are significant in applications such as missile or satellite carried infrared image sensing arrays.